Mechanical joints can be fabricated in a number of ways, all of which can be classified as either temporary or permanent. Temporary joints include, for example, screw threads, clamps, and the like, and permanent joints include, for example, brazed, welded, adhesively bonded, riveted, and the like.
It often happens that two or more structural members must be joined together, or an accessory, such as a cable strap, must be joined to a structural member but the joining point is relatively inaccessible. For example, in an aircraft structure, two or more members must often be joined together at a point that is completely inaccessible from one side and only inconveniently accessible from the other side, as for example, near an access port in a bulkhead which is positioned a short distance away from the members to be joined.
If the joining point lies directly in front of an access port, it is a simple matter to drill through the members to be joined, then join them together using, for example, a self-tapping screw or a blind rivet. If, however, the joining point is not directly accessible, use of a self-tapping screw is well nigh impossible, while use of blind rivets may be precluded due to the size of the rivet tool.
Blind rivets are available in three general types: screw, mandrel and explosive. In the explosive type an explosive charge in the point is set off by a special hot iron: the explosion expands the point and sets the rivet. In the mandrel type, the rivet is set as the mandrel is pulled through. The explosive and the mandrel types of blind rivets have certain drawbacks which limit their usefulness in fabrication or repair of an aircraft structure. For example, the explosive type cannot be used in or near a potentially explosive or inflammable environment, while the mandrel type cannot be used where a structure must be sealed, inasmuch as the set rivet is hollow. Accordingly, for many aircraft applications, screw type rivets are used. This type of rivet, illustrated hereinafter, comprises a threaded mandrel, a bushing having an integral rivet head and a threaded bore, and an expansible sleeve. In use the threaded rivet is inserted into a drilled hole in a member so that the head is butted against the front side of the member, a special driving tool is positioned over the rivet head, the mandrel is screwed through the bushing and, when the rivet is set, the mandrel is broken off flush with the top of the rivet head. The bushing is longer than the total thickness of the members to be joined together and is tapered at its outer end. As the mandrel is screwed through the bushing, it urges the sleeve onto the tapered portion of the bushing and over the outside surface of the bushing. The sleeve becomes compressed between the head of the threaded mandrel and the backside of the members being joined, thus "setting" the rivet. The resulting rivet is solid and strong.
The holes for the screw type blind rivets may be drilled in relatively inaccessible areas using a specialty drill, known in the trade as a "foot" drill. This drill has a lateral extension for holding the drill bit at some distance away from the motor housing.
In practice, once a hole is drilled in a relatively inaccessible place and a screw type rivet is inserted into the hole, it frequently happens that the special driving tool cannot be positioned so that it holds the rivet perpendicular, or nearly so, to the members being joined together. If the special driving tool holds, drives and sets the screw type rivet at an angle, it elongates and distorts the rivet hole. These rivets, driven and set at an angle away from the perpendicular will often work loose.
Accordingly, it is an object of the present invention to provide means for driving and setting a screw type rivet in a relatively inaccessible place.
Other objects and advantages of the present invention will be apparent to those skilled in the art from the following description of the invention.